In a carriage printer, such as an inkjet carriage printer, a printhead is mounted in a carriage that is moved back and forth across the region of printing. To print an image on a sheet of paper or other print medium, the medium is advanced a given nominal distance along a media advance direction and then stopped. While the medium is stopped and supported on a platen, the printhead carriage is moved in a direction that is substantially perpendicular to the media advance direction as marks are controllably made by marking elements on the medium—for example by ejecting drops from an inkjet printhead. After the carriage has printed a swath of the image while traversing the print medium, the medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
FIG. 1 shows a schematic side view of a conventional carriage printer having a so-called L-shaped paper path. A variety of rollers are used to advance the medium through the printer. In this example, a pick roller 350 moves the first piece or sheet 371 of a stack 370 of paper (also generically called recording medium herein) at media input support 320 from paper load entry direction 301 toward media retention plate 340. The first piece 371 of recording medium is then moved by feed roller 312 and idler roller(s) 323 to advance through the print region 303, and from there to a discharge roller 324 and star wheel(s) 325. Carriage 200 moves a printhead die 251 along a carriage scan direction that is into the plane of FIG. 1 and ink drops 270 are controllably ejected to print an image as the carriage is moved. The motion of carriage 200 is guided by carriage guide 382, which is a round rod, for example, that is disposed along the carriage scan direction. Supporting the first piece 371 of recording medium at print region 303 is a platen 390. In order to facilitate the printing of borderless prints where the image is printed to the edges of the recording medium, platen 390 can have support ribs 394 in between which is disposed an absorbent medium 392 to catch ink drops that are oversprayed beyond the edges of the recording medium. The top surfaces of support ribs 394 are located at substantially a same level, so that they define a plane of the print region 303, i.e. the plane of support of the recording medium in the print region 303.
In order for the ink drops 270 to land accurately at their intended positions on first piece 371 of recording medium, it is important for the carriage 200 to move uniformly along the carriage scan direction. However, it is found that the carriage guide 382 can be undesirably set into vibration, for example along vibration direction 385. Such vibration of the carriage guide 382 can cause nonuniform motion of the carriage 200 and the printhead die 251, so that the ink drops do not land accurately at their intended positions, thereby degrading print quality.
What is needed is a simple, low cost way of reducing vibration of the carriage guide so that the carriage printer can reliably provide high quality printing.